Black Widows

This flyer is from Santa Clara County Vector Control. 
Black Widows live under buildings, under rocks and in woodpiles and dense vegetation.  The can also be in storage sheds, under patio furniture and in dark hidden corners.  We use to have them in Cupertino, in the outside tool closet.  Bites cause mild to sever pain.  The can also cause muscle spasms, increased blood pressure and difficulty breathing.  For most people, symptoms will subside after a couple days.  Fr children and elderly medical attention should be sought.  A cold pack will lessen the pain.  Bites can be prevented by being alert moving a wood pile, shake out clothes that have been stored, dust and vacuum where spiders may hide, clean clutter in the garage, seal cracksk in windows and doors.
We also have tarantulas in our area.  They are shy and rarely bite.  When they do their bite is similar to a bee sting.  Brown Recluses are not in our area.  False Widows have mild venom.